For those who wondered why this is under Isekai Tag, I'll share my 50 cents:
異世界 - (Isekai) = 異 (Different/Strange) 世 (Society/Generation) 界 (World/Boundary)
By dictionary it can be referring to different world, parallel universe, alternative world.
If you on Earth and doing a documentary about Ants; it's Isekai
If you check germs under microscopic ; it's Isekai
Deep ocean? Isekai
Marvel Movies? Isekai although the place are all exact same on Earth + Fantasy.
Digimon? Isekai
Pokemon? Isekai
SAO? Living in dreams (games) also Isekai because it's different than reality.
When a normal citizen, entered the society of drugs dealer, violence and crime etc; you can related when someone said "This is different world than we used to live"
As long as it's "different" than our current "world" or "society" the usage of "isekai" is legitimate.
As for this manga, I believe their intention of using "Isekai" is due to "Nursery School".
I haven't check the history yet but back in medieval age, or similar-fantasy-like genre, nursery school was never existed.
Maybe there is an orphan community or church or etc etc, but nursery school is like university; which only existed around 1200-1800 years ago; I think?
TL;DR - To understand the genre, look back at the word's origin.
INB4; there's a harem tag but admin must have removed it to avoid confusion. Maybe the Isekai tag will be removed as the story getting cleared as the more chapters goes to fits readers perspective although it's not wrong.
